Conventional articles of athletic footwear generally include two primary elements, an upper and a sole structure. The upper is secured to the sole structure and forms a void on the interior of the footwear for securely and comfortably receiving a foot. The upper is generally formed from multiple elements that are stitched and adhesively bonded together to form a comfortable structure for receiving the foot. Conventional athletic footwear may include, for example, an exterior formed of leather and polymer textile materials that are resistant to abrasion and provide the footwear with a particular aesthetic. Foam materials may be located on the interior of the upper to enhance the comfort of the upper, and moisture-wicking textiles may be positioned adjacent the foot to limit the perspiration within the upper.
The sole structure attenuates ground reaction forces and absorbs energy as the footwear contacts the ground, and often incorporates multiple layers that are conventionally referred to as a midsole and an outsole. The midsole forms the middle layer of the sole and serves a variety of purposes that include controlling potentially harmful foot motions, such as over pronation, and shielding the foot from excessive ground reaction forces. The outsole forms the ground-contacting element of footwear and is usually fashioned from a durable, wear resistant material that includes texturing to improve traction. The sole structure may also include an insole, which is a thin, cushioning member located within the upper and adjacent to a sole of the foot to enhance footwear comfort.
The upper and sole structure of most conventional articles of footwear are permanently secured together through adhesive bonding or stitching, for example. Accordingly, wear or damage occurring to either the upper or sole structure may require that the entire article of footwear be discarded. In addition, sole structures are generally configured for use during specific activities, particularly with athletic footwear. For example, a sole structure may incorporate pronation control elements that are beneficial for running, stability elements for court-style activities, or relatively soft cushioning for walking. A sole structure that is configured for one athletic activity, such as long-distance running, may not be suitable for use during another athletic activity, such as tennis. Each different type of sole structure, therefore, requires a distinct upper in footwear where the upper and sole structure are permanently secured together.
In contrast with the conventional article of footwear that includes a permanently secured upper and sole structure, footwear configurations embodying an upper and detachable sole structure have been proposed. U.S. Pat. No. 6,023,857 to Vizy et al. discloses footwear with a permanently attached upper and outsole that includes a separate midsole and heel counter structure, which is removable from the upper. U.S. Pat. No. 5,083,385 to Halford and U.S. Pat. No. 4,974,344 to Ching both disclose an outsole structure that is detachable from the remainder of the footwear. Finally, U.S. Pat. Nos. 6,023,859 and 5,799,417 to Burke et al. disclose an article of footwear with removable and exchangeable inserts that are positioned between the upper and a lower portion of the sole structure. The inserts protrude through the lower portion of the sole structure to provide a ground-contacting surface.